Hydrostatic seal for rotary machine tool spindles

ABSTRACT

A hydrostatic seal is provided for machine tool headstocks having rotary, or rotary and translatable, tool spindles. A pressurized air film is formed between opposite sides of a thrust ring and adjacent hydrostatic seal bearings, forming a substantially frictionless seal and preventing oil leakage from around the tool spindle.

United States Patent 1 3,698,725

Klabunde 51 Oct. 17, 1972 [54] HYDROSTATIC SEAL FOR ROTARY 3,103,3649/1963 Macks et al. ..274/39 MACHINE TOOL SPINDLES 3,132,903 5/1964 Webb..308/9 [72] inventor: itgenvifldor Klabunde, Fond du Primary ExaminerEdgar w. Geoghegan Assistant Examiner-Frank Susko [73] Assignee:Giddings 8: Lewis, Inc., Fond du Attorney-Wolfe, Hubbard, Leydig,Voit&0sann Lac, Wis. [22] Filed: Jan. 13, 1971 [571d 1 f i A by rostaticsea is provi ed or machine tool head- [21] Appl' 106,156 stocks havingrotary, or rotary and translatable, tool spindles. A pressurized airfilm is formed between op- [52] 0.8. CI ..277/74, 277/94 po ite sides ofa thrust ring and adjacent hydrostatic [51] Int. Cl ..B65d 53/00, FlSj15/l6, Fl6j 15/34 seal bearings, forming a substantially frictionlessseal [58] Field of Search ..277/74 X, 81, 94 and preventing oil leakagefrom around the tool spindle.

[56] References Cited UNITED STATES PATENTS 13 Claims, 7 Drawing Figures2,696,410 211,9543 spsns iaqtls tyfil W flu' 1% T ma t: 4,

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IIYDROSTATIC SEAL FOR ROTARY MACHINE TOOL SPINDLES This inventionrelates generally to rotary seals and more particularly concernshydrostatic seals for use in machine tool headstocks having rotary, orrotary and translatable, tool spindles.

Machine tool designers have long been faced with a number of specialproblems concerning leakage of lubricating oil and other materialthrough seals located in the annular clearance space between machinetool spindles, spindle sleeves arid their support housings. Some sealspresently in use are highly susceptible to wear. Others are susceptibleto damage or breakage due to entry of contaminants such as dust, gritand cutting tool chips. In either event, there is resultant oil leakagewhich requires clean-up as well as replacement of lost fluid, andhousekeeping chores which machine tool users are reluctant to accept intheir machine shop operations.

The foregoing problems are aggravated in modern spindle headstockassemblies where relatively large quantities of oil under positivepressure are used to provide not only lubrication, but also assemblycooling and preloading of spindle bearings. Even when the machine is notbeing operated, oil may collect behind the seal with eventual leakageresulting.

Yet another problem isencountered in the use of seal assemblies havingfrictionally engaging parts such as resilient seal rings which engagethe rotating surface of a spindle. Such friction contributes not only tothe inevitable wear of the parts involved, with the resultant fluidleakage problems described, but also generates heat. This, in turn,tends to introduce distortions in the workpiece or headstock parts,which is unacceptable when highly precise machining is required.

It is therefore the general object of this invention to provide animproved seal between the spindle and housing of a machine toolheadstock.

More specifically, it is an object of the invention to provide a sealbetween a spindle assembly and the housing of a machine tool headstockwhich will effectively prevent leakage of oil or cooling fluid from theheadstock under any normal head of pressure that may build up behind theseal.

Another object is to provide a seal of the character set forth abovewhich can be used with a variety of machine tool headstocks.

Another object is to provide a seal of the described character whichwill be affected by axial or radial runout during operation of theassociated headstock.

Yet another object is to provide a seal of the 7 described characterwhich will not be damaged by dust, grit, chips or other contaminants andwhich will prevent their entry into the headstock interior.

Still another object of the invention is to provide a seal for a rotarytool headstock which generates little or no heat through frictionalcontact of relatively moving parts.

An additional object is to provide a seal for a headstock which willprevent fluid leakage even when the machine is not operating but whenfluid has collected behind the seal so as to provide a static headpressure thereupon. A further object is to provide a hydrostatic sealrequiring a relatively low volume of pressurized air for operation.

A related object is to provide a hydrostatic seal which will not pollutethe surrounding environment with an oil spray under normal operatingconditions.

Still another object of the invention is to provide an improved seal fora rotary machine tool headstock which is compact in its dimensions,reliable and rugged in its design, durable in operation, and relativelyinexpensive to manufacture.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings, in which:

FIG. 1 is a perspective view of an illustrative machine tool containingthe novel headstock seal embodying the present invention;

FIG. 2 is an enlarged fragmentary sectional view taken axially of thespindle and substantially in the plane of the line 22 in FIG. 1 showinga portion of the headstock with the seal incorporated therein;

FIG. 3 is an enlarged fragmentary sectional view taken substantially inthe plane of the line 3-3 of FIG. 1 showing the vacuum scavenger line;

FIG. 4 is a further enlarged fragmentary sectional view similar to FIG.2 and taken substantially in the plane of the line 2-2 in FIG. I showingthe seal elements in greater detail;

FIG. 5 is a fragmentary view of the headstock front showing, in abroken-away form, parts of the headstock and seal;

FIG. 6 is an enlarged fragmentary sectional view similar to FIG. 4 andshowing an alternate embodiment of the invention, and

FIG. 7 is a sectional view similar to FIG. 2 but showing the headstockseal as used in a headstock having an axially extensible spindle.

While the invention will be described in connection with an exemplaryembodiment, it will be understood that it is not intended to limit theinvention to that embodiment, On the contrary, it is intended to coverall alternatives, modifications and equivalents as may be includedwithin the spirit and scope of the invention.

Turning first to FIG. 1, the invention is there exemplified in anillustrative machine tool 10 having a headstock 11 with a spindlemounted therein for rotational movement. The machine tool 10 happens inthis instance to be a large contour milling machine such, for example,as the one described in US. Pat. No. Re. 26,393. It will be understoodthat the invention may be installed in other machine tools with equalfacility. The illustrated machine tool 10 is adapted to engage aworkpiece (not shown) secured to a relatively heavy work support 12mounted upon a bed 14 adjacent the machine. The machine tool 10comprises a relatively long fixed base 15 which carries a sliding base16 adapted for movement along the fixed base 15. The

sliding base 16, in turn, supports a swivel base 17 adapted to beshifted in an arcuate path along the top surface of the sliding base 16.Fixed to the top of the swivel base 17 is a column 18 which serves as asupport for a vertical saddle 19. The latter is mounted for verticalsliding movement on the column and carries, in turn, a swivel saddle 20.The swivel saddle 20 supports the headstock 11 so as to permit arcuatemovement of the latter in a vertical plane.

From the above, it will be seen that the headstock 11 is mounted formovement on five axes relative to the workpiece. Such movement includestranslation on three coordinate axes X, Y and Z and swivel motion abouthorizontal and vertical axes A and B, thereby permitting the headstock11 and its cutting tool 23 to be oriented in any desired positionrelative to the workpiece. Movements of the headstock 11 and the cuttingtool 23 carried thereupon may be controlled through numerical controlequipment (not shown) in a well known manner. As best seen in FIG. 2,the headstock 11 includes a housing 30 having a bore 31 therein. Withinthe bore 31, a cylindrical quill 32 is supported. A spindle isjournalled for rotation within the quill 32 by anti-friction bearings 35and 36, and is driven by a bull gear 37. To support the spindle 34 withgreat precision even under heavy cutting loads and low spindlerotational speeds, the spindle bearings 35 and 36 may be preloaded toprevent vibration and chatter as the tool engages the workpiece. Thisbearing preloading is described in U.S. Pat. No. 3,21 1,060. Briefly,the bearing preload piston 39 is selectively urged by fluid pressureeither to the right or to the left to apply either a relatively light ora relatively heavy preload to the bearings 35 and 36.

To provide cooling for the headstock parts, refrigerated oil iscirculated through the oil lines and passages 43, in the generaldirection indicated by arrows. The large quantities of pressurized andrefrigerated oil so circulated also provide lubrication for the spindlebearings 35 and 36 through the lubrication passages 44.

It will thus be appreciated that, when the machine tool containing thenovel seals is in operation and spindle 34 is rotating, relatively largequantities of pressurized hydraulic fluid and pressurized lubricatingand cooling oil may be circulated through the headstock 11. When theheadstock 11 is rotated into an. inclined position so that the frontbearing 35 is located at a lower position than the rear bearing 36,quantities of fluid may collect adjacent the lower bearing 35, creatinga head of static fluid pressure in the lower or front portion of theheadstock. Such fluid collection and static head development may occureven though the hydraulic and oil pressurization systems are not inoperation.

in accordance with the invention, a novel hydrostatic seal 45 ispresented and is installed so as to prevent the leakage of fluids fromthe headstock 11. The seal also prevents the entrance of dust andworkpiece chips from entering into the headstock interior and isessentially frictionless in operation.

The hydrostatic seal 45 includes an annular thrust element 46 (FIGS.2-4) fixed to the spindle 34 for rotation bodily therewith. Theillustrated thrust element 46 is of generally rectangular cross section,and is provided with two side surfaces 47 and 48 extending normally andradially above the spindle surface 49. The hydrostatic seal 45 alsoincludes, in addition to the thrust element, two stationary opposingporous seal bearings 51 and 52 located on opposite sides of the thrustelement and closely adjacent the radial surfaces 47 and 48 thereof.These endless annular seal bearings are preferably formed of porousgraphitic carbon which, in the present instance, has a permeability ofabout 25,000 microdarcies. Such graphitic carbon is self-lubricating andis resistant to clogging, owing to the large number of individual airpassages formed therein. Material of this type is commercially availablefrom the Pure Carbon Company of St. Marys, Pa., under the trade namePurebon P-2W. in the illustrated embodiment of the invention, thebearings 51 and 52 are securely bonded to the surrounding supportstructure 64 in any convenient manner which will prevent leakage of airaround the peripheries 51 a and 52a, respectively, of the bearings 51and 52.

In further accordance with the invention, means are provided forsupplying pressurized air through the porous hydrostatic seal bearings,thereby creating and maintaining thin, continuous annular pressurizedair films in the clearance spaces 54 and 55 between the bearing 51 andthrust element side surface 47, and between the bearing 52 and thrustelement side surface 48, respectively, as seen particularly in FIG. 4.In the illustrated embodiment of the invention, the means for supplyingthe pressurized air includes an air pressure source (not shown) and theair passage 57. The air passage 57 communicates with a pair of annularpassages 58 for distribution of pressurized air to the rear of eachporous seal bearing 51 and 52; the delivered pressurized air seepsthrough the seal bearings 51 and 52 to form the described air film inthe spaces 54 and 55. These thin annular air films are of equal pressureand serve to effectively seal the headstock so as to prevent the leakageof oil along the spindle surface and past the thrust element 46.Moreover, external contaminants such as dust, cutting fluids, andworkpiece chips are excluded from entering the headstock by the exhaustflow of air in the direction indicated by the arrows 56 and 56a and bythe pressurized film of air.

Experimentation has shown that, to provide relatively ideal sealingconditions, the thrust element 46 and seal bearings 51 and 52 should bespaced apart from each other by a predetermined distance. A distance ofabout 0.00045 to 0.00050 inches between the surfaces 47 and 48 of thethrust element 46 and the adjacent seal bearing surfaces 59 and 59aprovide effective sealmg.

Experimentation has further shown that spacing distances of from 0.00035inches to about 0.00150 inches can provide satisfactory sealing. Thesesmall distances are in part accurately obtained by finishing theadjacent surfaces 47, 48, 59, 59a of both the thrust element 46 and theseal bearings 51 and 52 to a surface tolerance of $0.0002 inches, bothparallel and flat, after the bearings have been bonded to thesurrounding support structure 53. To prevent passage or sea] bearingclogging and resultant seal malfunctions, it is recommended thatfiltered and dehydrated compressed air be supplied at a standard shoppressure of between 60 and 120 psi; psi has been found to provide goodoperating results.

Return of oil from the vicinity of the air film is accomplished by thescavenger line 50b shown in FIG. 3. it is a feature of the inventionthat little or no leakage will occur through the seal assembly if thepressurized air supply is accidentally or purposely disconnected eventhough oil surrounding the seal is under a head of pressure. In such acircumstance, the pressurized air film will dissipate but, therelatively small clearances by the opposed surfaces of the seal provideresistance to passage of oil. In addition the carbon graphite sealbearings 51 and 52 will become saturated with oil causing additionalresistance to leakage. Further, in the event that the air supply to theseal is terminated, only slight frictional forces will be encounteredsince the carbon graphite bearings retain their lubricating qualities.

As an alternate construction, the seal bearing members 51 and 52 may beformed of suitable non-porous material perforated to provide therequisite overall permeality of about 25,000 microdarcies so as to allowgeneration and maintenance of the sealing air cushions.

In accordance with a further aspect of the invention, the thrust elementmay, if desired, be constructed to be capable of axial motion along thespindle surface 49. To these ends, the thrust element 46 illustrated inFIGS. 2-5 comprises an annular resilient sealing member such as aquad-ring 60 of substantially rectangular cross-sectional shape and anannular thrust ring 61 surrounding the quad-ring sealing member 60. Toprovide a firm sealing seat for the quad-ring 60, the thrust ring 61 isprovided with an annular groove 62 of substantially rectangularcross-sectional shape. The seal element engages the surface 49 of thespindle along one of its four sides, and wipes the surface clean of oilor other material when the quad-ring 60 and thrust ring 61 are togetherforced axially along the spindle 34. The necessity for accuratelylocating the thrust element axially upon the spindle 34 is alsoeliminated,

since this sea] connection permits the thrust ring 61 to be axiallypositioned to conform to the surrounding structure during assembly ofthe device. The seal connection also permits relative motion between thethrust ring 61 and the spindle 34 after assembly and during use, such asmay be experienced due to relative expansion of the headstockcomponents, spindle bearing wear, and changes in the spindle bearingpreload.

It is a feature of the invention that the interior diameter of thethrust ring 61 is about 0.001 inches larger than the adjacentdiameter ofthe spindle 34, thereby providing a sealing effect between the thrustring and spindle itself, and preventing damage to the seal element 60 byimpingement of foreign matter such as dust and chips thereupon.

Assembly and retention of the described seal 45 upon a headstock (FIGS.2-4) is easily accomplished. A seal housing 64 is formed with acylindrical pilot surface 65 which surface 65 is adapted to mate with acounterbore 66 so as to center the housing 64 relative to the axis ofthe headstock 11. The seal housing 64 is formed with concentriccounterbores 68 and 69. A generally annular ring 70 is located withinthe counterbore 69, and is provided with a radial face 71 opposing andspaced from the other counterbore 68, thereby forming a generallyrectangular annular recess 72 into which the seal assembly fits. Theseal housing 64 is retained upon the quill by a plurality of bolts 73which are threaded into the quill and tightened into place with equaltorque, thereby obtaining and assuring equal cross-sectional dimensionsfor all parts and part clearances in the seal assembly. The mostinterior bore 74 FIGS. 4,5) of the seal housing 64, through which thespindle 34 projects, is preferably from 0.004 to 0.006

inches larger than the adjacent diameter of the spindle 34 itself,thereby providing a preliminary sealing effect against the entrance ofchips or other foreign matter into the seal assembly and headstockinterior.

An alternate embodiment of the invention is illustrated in FIG. 6,wherein is included a spindle mounted in a bearing 81 for rotationalmovement only. Formed upon the spindle 80 is a flange 82 having a sidesurface 83 for cooperation with a porous annular seal bearing 84. Air issupplied to the rear of the bearing 84 through appropriate passages 85to form the sealing air film in the manner described above. To provide acontinuous seal for these passages 85, seals 86 and 87 of a diameterlarger than the diameter of the spindle 80 are provided, and bearagainst the housing 64 and bearing support 88.

In accordance with another aspect of the invention, the novelhydrostatic seal 45 may be conveniently mounted for use in a headstock90 equipped with a spindle 91 which is mounted for relatively extendedaxial motion as shown in FIG. 7. In the illustrated headstock 90, thespindle 91 is supported for both rotary and axial movement byhydrostatic bearings 93. The axial traverse movement of the spindle 91is used in drilling, boring, tapping and like operations. When thespindle 91 is extended or moved to the left the thrust element 46,comprising the sealing member 60 and thrust ring 61 rides over thespindle surface 49 as described above, and maintains its relativeposition between the bearings 51 and 52. Pressurized air is delivered tothe seal by convenient means as though ap propriate hosing and taps 95.Assembly of the seal 45 in this or other headstocks may be accomplishedin a manner similar to that used in connection with the typicalheadstock 45 illustrated in FIGS. 2-5.

I claim as my invention:

1. In a machine tool having a head stock, a spindle, and means rotatablysupporting the spindle within the head stock, a hydrostatic sealpreventing the flow of liquid between said spindle and spindle supportmeans, said seal comprising an annular thrust member extending radiallyoutward from said spindle, said thrust member being formed with at leastone bearing surface, a nonrotatable porous hydrostatic seal bearingmounted within said spindle support means, said porous bearing having atleast one bearing surface in closely spaced relation to said thrustmember bearing surface, I and means for supplying pressurized airthrough the porous hydrostatic seal bearing to provide an air cushionbetween the closely spaced surfaces of said bearing and thrust memberwith a pressure sufficient to prevent leakage of liquid along thespindle past the thrust member.

2. In a machine tool having a head stock, a spindle, and means rotatablysupporting the spindle within said head stock, a hydrostatic sealpreventing the flow of liquids between said spindle and said spindlesupport means, said seal comprising an annular thrust member mountedupon said spindle for rotation therewith and having surfaces extendingnormally and radially outward from the spindle, a pair of nonrotatableporous hydrostatic seal bearings mounted within said spindle supportmeans on opposite sides of said thrust member, said porous seal bearingseach having a surface which is closely adjacent one of said radialthrust member surfaces, and means for supplying pressurized air throughthe porous hydrostatic seal bearings to provide two opposing annular aircushions of substantially equal pressure and dimensions between eachporous bearing and therespective thrust member surface which creates asubstantially frictionless seal between said thrust member and saidbearings and prevents liquid from flowing along the spindle past thethrust member.

3. A device according to claim 2 wherein the thrust member comprises anannular grooved thrust ring and an annular sealing member sealinglyseated within the groove and engaging the surface of said spindle.

4. A device according to claim 2, wherein the thrust member comprises anannular resilient, quad-ring sealing member of substantially rectangularcross-sectional shape contacting said spindle along one side of saidrectangle, and an annular thrust ring of substantially rectangularcross-sectional shape surrounding the sealing member on its remainingthree cross-sectional sides.

5. A device according to claim 4, wherein said thrust ring and saidspindle are spaced apart from each other by said seal member by adistance of about 0.001 inches.

6. A device according to claim 2, wherein said thrust member may bemoved for a limited distance in an axial direction along the surface ofsaid spindle.

7. A device according to claim 2, wherein said hydrostatic seal bearingsare formed of porous graphite carbon having a permeability of about25,000 microdar- CleS.

8. A device according to claim 2, wherein said hydrostatic seal bearingsare formed of porous material having an overall permeability of about 25,000 microdarcies.

9. A device according to claim 2, wherein said hydrostatic seal bearingsare endless and annular in shape.

10. A device according to claim 2, wherein said air supply meansprovides air to said hydrostatic seal bearings at a pressure in therange from about 60 psi to about psi.

11. A device according to claim 2, wherein said thrust member and saidseal bearings are spaced from each other by a distance in the range fromabout 0.00035 inches to about 0.00150 inches.

12. A device according to claim 2, wherein said thrust member and saidseal bearings are spaced from each other by a distance in the range fromabout 0.00045 inches to about 0.00050 inches.

13. A hydrostatic sealfor machine tool spindle headstocks, comprisingthe combination of a rotatable spin-, die and a spindle support means,an annular thrust member mounted upon the spindle for rotation therewithand having bearing surfaces extending normally and radially with respectto said spindle, stationary porous hydrostatic seal bearings fixed tosaid spindle support means and having bearing surfaces located closelyadjacent the bearing surfaces of the thrust member, and means forsupplying pressurized air through said porous hydrostatic seal bearingsto provide air cushions between the bearings and thrust member surfaceswhich prevents the leakage of liquids from between said spindle andspindle support means.

l III t i

1. In a machine tool having a head stock, a spindle, and means rotatablysupporting the spindle within the head stock, a hydrostatic sealpreventing the flow of liquid between said spindle and spindle supportmeans, said seal comprising an annular thrust member extending radiallyoutward from said spindle, said thrust member being formed with at leastone bearing surface, a nonrotatable porous hydrostatic seal bearingmounted within said spindle support means, said porous bearing having atleast one bearing surface in closely spaced relation to said thrustmEmber bearing surface, and means for supplying pressurized air throughthe porous hydrostatic seal bearing to provide an air cushion betweenthe closely spaced surfaces of said bearing and thrust member with apressure sufficient to prevent leakage of liquid along the spindle pastthe thrust member.
 2. In a machine tool having a head stock, a spindle,and means rotatably supporting the spindle within said head stock, ahydrostatic seal preventing the flow of liquids between said spindle andsaid spindle support means, said seal comprising an annular thrustmember mounted upon said spindle for rotation therewith and havingsurfaces extending normally and radially outward from the spindle, apair of nonrotatable porous hydrostatic seal bearings mounted withinsaid spindle support means on opposite sides of said thrust member, saidporous seal bearings each having a surface which is closely adjacent oneof said radial thrust member surfaces, and means for supplyingpressurized air through the porous hydrostatic seal bearings to providetwo opposing annular air cushions of substantially equal pressure anddimensions between each porous bearing and the respective thrust membersurface which creates a substantially frictionless seal between saidthrust member and said bearings and prevents liquid from flowing alongthe spindle past the thrust member.
 3. A device according to claim 2wherein the thrust member comprises an annular grooved thrust ring andan annular sealing member sealingly seated within the groove andengaging the surface of said spindle.
 4. A device according to claim 2,wherein the thrust member comprises an annular resilient, quad-ringsealing member of substantially rectangular cross-sectional shapecontacting said spindle along one side of said rectangle, and an annularthrust ring of substantially rectangular cross-sectional shapesurrounding the sealing member on its remaining three cross-sectionalsides.
 5. A device according to claim 4, wherein said thrust ring andsaid spindle are spaced apart from each other by said seal member by adistance of about 0.001 inches.
 6. A device according to claim 2,wherein said thrust member may be moved for a limited distance in anaxial direction along the surface of said spindle.
 7. A device accordingto claim 2, wherein said hydrostatic seal bearings are formed of porousgraphite carbon having a permeability of about 25,000 microdarcies.
 8. Adevice according to claim 2, wherein said hydrostatic seal bearings areformed of porous material having an overall permeability of about 25,000microdarcies.
 9. A device according to claim 2, wherein said hydrostaticseal bearings are endless and annular in shape.
 10. A device accordingto claim 2, wherein said air supply means provides air to saidhydrostatic seal bearings at a pressure in the range from about 60 psito about 120 psi.
 11. A device according to claim 2, wherein said thrustmember and said seal bearings are spaced from each other by a distancein the range from about 0.00035 inches to about 0.00150 inches.
 12. Adevice according to claim 2, wherein said thrust member and said sealbearings are spaced from each other by a distance in the range fromabout 0.00045 inches to about 0.00050 inches.
 13. A hydrostatic seal formachine tool spindle headstocks, comprising the combination of arotatable spindle and a spindle support means, an annular thrust membermounted upon the spindle for rotation therewith and having bearingsurfaces extending normally and radially with respect to said spindle,stationary porous hydrostatic seal bearings fixed to said spindlesupport means and having bearing surfaces located closely adjacent thebearing surfaces of the thrust member, and means for supplyingpressurized air through said porous hydrostatic seal bearings to provideair cushions between the bearings and thrust member surfaces whichprevents the leakage of liquids from between said spindle and spindlesupport means.